This invention relates to a method and apparatus for increasing the speed at which a fork lift truck travels and/or the lowering speed of the truck's forks when the forks are unloaded or substantially unloaded.
Industry braking standards require that a loaded truck stop within a predetermined distance or comply with a well known drawbar drag test. Most fork lift trucks are not provided with a weight sensor for determining if the truck is loaded; therefore, the maximum speed of the truck does not change based upon the load status of the forks. If the truck is not loaded, then there is excess braking capacity and the truck could be allowed to travel at a faster speed and still meet industry braking requirements.
The forks are raised and lowered by at least one hydraulic cylinder. It is known to provide a mechanical proportional valve to control the flow of hydraulic fluid to and from that cylinder. Operation of the valve is controlled by an operator via a control handle. The hydraulic system including the valve is designed so as to allow the forks, when fully loaded, to descend at a limited rate. No provision is provided to allow the forks to be lowered at an increased rate when the forks are unloaded.
There is a need for an improved method and apparatus for increasing the speed at which a fork lift truck travels and/or the lowering speed of the truck's forks when the forks are unloaded or substantially unloaded so as to increase productivity.